Monoflow valves are used to prevent backflow in pressurized flow systems and typically such valves utilize a ball and seat which acts to allow flow in one direction and resist flow in the opposite direction. This type of valve is frequently referred to as a mono-flow ball valve. The resistance to backflow is usually accomplished by maintaining the ball against an internal seat to close the flow passage. A sufficient pressure gradient in one direction against the ball will overcome the force maintaining the ball against the seat and allow flow.
There are valve-controlled pressurized fluid flow systems in which metal-corrosive acids such as hydrochloric acid, hydrofluoric acid, sulphuric acid and the like are being handled. An example of this type of system is disclosed in U.S. Pat. Nos. 3,997,114 and 4,046,321, assigned to the assignee of the present invention.
A problem that can occur with monoflow ball valves is that the ball may become lodged against the seat and prevent flow in either direction. The likelihood of this occurring is increased in a flow system in which acid or caustic fluids are being pumped.